Process for olefin oligomerization

ABSTRACT

A process for preparing a substantially linear olefinic hydrocarbon mixture is described in which a lower olefin feed comprising one or more C 3  to C 6  lower olefins is contacted in the presence of water and under olefin oligomerization conditions with a catalyst comprising surface-deactivated ZSM-23.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of InternationalApplication No. PCT/US03/09516, filed Mar. 28, 2003, which claims thebenefit of Provisional Application No. 60/368,864, filed Mar. 29, 2002.These applications are incorporated herein by reference.

FIELD

This invention relates to lower olefin oligomerization employing amolecular sieve to produce a higher olefin mixture, more specifically asubstantially linear olefinic hydrocarbon mixture.

BACKGROUND

Olefinic hydrocarbons are employed as starting materials in thehydroformylation, or oxo, process, for the eventual manufacture ofnumerous valuable products, e.g., alcohols, esters and ethers derivedtherefrom, aldehydes, and acids. Additionally, olefinic hydrocarbons areemployed as reactants in the alkylation of aromatic hydrocarbons,specifically for the manufacture of linear alkyl aromatics and linearalkylaryl sulfonates, for eventual formulation into surfactants used ina wide variety of applications. In many of these end uses, linear orlightly branched hydrocarbon chains have advantages compared with moreheavily branched chains. In the oxo process, olefins with linear orlightly branched structures are more reactive than those with heavilybranched chains and, for a given degree of branching, certain isomersare more reactive than others. In surfactants produced from alkylationof olefinic hydrocarbons and sulfonation of the alkyl aromatic product,highly branched materials exhibit very poor biodegradability. However,linear alkylaryl sulfonates often are not highly effective as cleaningagents. Use of surfactants produced from lightly branched olefinoligomers in detergent formulations is advantageous because suchsurfactants exhibit acceptable cleaning properties and yet arerelatively biodegradable.

Processes for oligomerizing olefins to produce a hydrocarbon materialwith a reduced degree of branching are well known in the art, forexample as described in U.S. Pat. Nos. 4,855,527; 4,870,038; 5,026,933;5,284,989; 6,013,851; and 6,300,536.

U.S. Pat. No. 4,855,527 describes a process for producing high molecularweight essentially linear hydrocarbon oligomers from a lower olefinfeedstock by employing a shape selective crystalline silicate catalyst(ZSM-23) which is surface deactivated.

U.S. Pat. No. 4,870,038 discloses a process for producing substantiallylinear hydrocarbons by oligomerizing propylene or butene by employing asurface inactivated, but internally active, ZSM-23 metallosilicatezeolite catalyst.

U.S. Pat. No. 5,026,933 teaches a process for producing substantiallylinear hydrocarbons by oligomerizing a C₂-C₈ olefin with siliceousacidic ZSM-23 zeolite having Brönsted acid activity; wherein the zeolitehas acidic pore activity and wherein the zeolite surface is renderedsubstantially inactive for acidic reactions.

U.S. Pat. No. 5,284,989 is directed to a process for producingsubstantially linear hydrocarbons by oligomerizing a lower olefin withacidic aluminosilicate ZSM-23 zeolite having Brönsted acid activity;wherein the zeolite has acidic pore activity and wherein the zeolitesurface is surface-deactivated for acidic reactions by contacting withoxalic acid.

U.S. Pat. No. 5,874,661 teaches that contacting a branched olefinichydrocarbon material with a catalyst in the form of a molecular sievehaving a 10-membered ring pore structure reduces the degree of branchingof the material.

U.S. Pat. Nos. 6,013,851 and 6,300,536 provide a process for theoligomerization of an olefin feed with a molecular sieve catalyst, inwhich a zeolite surface layer is deposited on each particle of themolecular sieve, the zeolite containing silicon and at least one otherselected element, the zeolite of the surface layer being of the samecrystalline structure as the core and having a higher silicon:selectedelement ratio than that of the core. The resulting product is an olefinoligomer hydrocarbon material having a reduced degree of branching.

Hydration of an olefin feedstock in a conventional oligomerizationprocess has been recognized in the art. U.S. Pat. No. 5,672,800discloses that by using a hydrated alkene-containing feedstock in analkene oligomerization process, the yields of higher molecular weightalkenes can be increased, and the catalyst becomes deactivated moreslowly. U.S. Pat. No. 6,013,851, discussed previously, also describeshydration of an oligomerization feed.

It would be desirable to prolong the life of the catalyst and to controlthe degree of branching in an oligomerization process to produce asubstantially linear olefin hydrocarbon product useful in a wide varietyof end use applications.

SUMMARY

The present invention is directed to a process for preparing asubstantially linear olefinic hydrocarbon mixture comprising contactinga feed comprising one or more C₃ to C₆ lower olefins in the presence ofwater and under olefin oligomerization conditions with a catalystcomprising surface-deactivated ZSM-23.

In one embodiment, the ZSM-23 is surface deactivated with a stericallyhindered nitrogenous base, such as 2,4,6-collidine.

Typically, the concentration of water in the feedstock is in the rangeof from about 25 ppm to about 1000 ppm; such as from about 100 ppm toabout 750 ppm, for example about 575 ppm to about 625 ppm. Inparticular, the feedstock may be water saturated.

Conveniently, the feedstock comprises a mixture of olefins selected frompropylene, butene and mixtures thereof, and in one embodiment the moleratio of propylene to butene in the feedstock is in the range of about99:1 to about 1:99.

Conveniently, the water and feed are contacted at a temperature in therange of from about 20° C. to about 60° C.

Conveniently, the substantially linear olefinic hydrocarbon producedfrom the oligimerization process is a olefinic hydrocarbon mixturecomprising at least 5 wt %, such as at least 20 wt %, for example atleast 85 wt %, of mono-olefin oligomers of the empirical formula:C_(n)H_(2n)where n is greater than or equal to 6, said mono-olefin oligomerscomprising at least 20 percent by weight of olefins having at least 12carbon atoms, said olefins having at least 12 carbon atoms having anaverage of from 0.8 to 2.0 C₁-C₃ alkyl branches per carbon chain.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention provides a process for preparing a substantiallylinear olefinic hydrocarbon mixture by contacting a lower olefin feed inthe presence of water and under olefin oligomerization conditions with acatalyst comprising surface-deactivated ZSM-23. The effect of the wateraddition is a decreased catalyst deactivation rate due to improved heatdissipation, resulting in prolonging the useful life of the catalyst,and a reduction in the degree of branching of the higher olefinsproduced as a product of the oligomerization process.

Catalyst

The oligomerization catalyst used in the process of the inventioncomprises ZSM-23 which has been surface deactivated, conveniently bytreatment with a sterically hindered nitrogenous base.

ZSM-23 and its characteristic X-ray diffraction pattern are described indetail in U.S. Pat. No. 4,076,842, the entire contents of which areincorporated herein by reference. ZSM-23 is a molecular sieve having apore size of 4.5×5.2 Angstroms, such as to freely sorb normal hexane butto provide constrained access to larger molecules. Typically, the ZSM-23employed is an aluminosilicate having a silica-to-alumina molar ratio ofat least 12 and acid cracking activity (alpha value) of about 10 to 300.In one embodiment, the ZSM-23 employed has an alpha value of about 25and a crystal size of less than 0.1 micron and is convenientlycomposited with a binder, such as alumina. The catalyst may be in theform of cylindrical extrudates of about 1 to 5 mm in diameter.

Surface deactivation of the ZSM-23 employed in the present process isconveniently achieved by treatment with a sterically hinderednitrogenous base, whereby surface acid sites are neutralized withoutsignificant reduction in the internal acid activity of the zeolite. Thedegree of steric hindrance of the basic nitrogen compound should besufficient to prevent entry of the compound into the internal pores ofthe catalyst, that is compound should have a minimum cross-sectionaldiameter greater than the effective pore size of the zeolite to betreated; i.e., greater than 5 Angstroms. However, excessive sterichindrance may prevent effective or complete interaction between thesurface acid sites of the molecular sieve and the selected basicspecies. Examples of suitable sterically hindered nitrogenous base areorganonitrogen compounds such as trialkyl pyridine compounds, and inparticular 2,4,6-collidine (2,4,6-trimethyl pyridine, gamma-collidine).

A process for surface deactivating a ZSM-23 catalyst with2,4,6-collidine is described in U.S. Pat. No. 5,026,933, the entirecontents of which are incorporated herein by reference.

Feedstock

The alkenes that can be oligomerized by the process of the invention areethene, propene, and linear or branched C₄ to C₁₂-alkenes. The alkenesare preferably C₃ to C₆-alkenes. The process is particularlyadvantageous for the oligomerization of propene and butenes and may beused for the oligomerization of a single alkene, or of mixtures ofalkenes of the same or of different carbon numbers. The alkene may ifdesired be diluted with another suitable gas, for example, a lowmolecular weight saturated hydrocarbon.

In one embodiment, the feedstock comprises a mixture of propylene andbutene, in which the mole ratio of propylene to butene is in the rangeof about 99:1 to about 1:99, such as in the range of about 49:51 toabout 5:95, for example in the range of about 35:65 to about 10:90.

Hydration

It has been discovered that when water is added to the above feedstockand/or to the reactor used in the oligomerization process, the life ofthe surface deactivated ZSM-23 catalyst is extended, as compared to thatof an identical catalyst to which no water has been added. Further,hydration of the feedstock results in a reduction of the degree ofbranching of the higher olefins produced.

The feedstock is advantageously hydrated prior to entering theoligomerization reactor. The desired proportion of water may beincorporated by saturating the feed at an appropriate temperature, e.g.,from 20 to 60° C., or by injecting water through a pump. For example,the feedstock may be passed through a thermostatted water saturator.Since the amount of water required to saturate the alkene feedstock willdepend upon the temperature of the feedstock, control of the waterconcentration is effected by appropriate control of the temperature ofthe feedstock. In one embodiment, the concentration of water in thefeedstock is in the range of from about 25 ppm to about 1000 ppm; suchas in the range of from about 100 ppm to about 750 ppm, for example inthe range of from about 575 ppm to about 625 ppm.

Process

Suitable oligomerization conditions include a temperature of about 160°C. to about 250° C., for example in the range of about 190° C. to about230° C., such as in the range of about 210° C. to about 220° C.; apressure in the range of about 500 psig (3447 kPa (gauge)) to about 1500psig (10342 kPa (gauge)), for example in the range of about 750 psig(5171 kPa (gauge)) to about 1250 psig (8618 kPa (gauge)), and a feedweight hour space velocity (WHSV) in the range of about 0.1 hr⁻¹ toabout 4.0 hr⁻¹, for example in the range of about 0.2 hr⁻¹ to about 3.0hr⁻¹, and such as in the range of about 1.75 hr⁻¹ to about 2.25 hr⁻¹.

Where surface deactivation is achieved by treatment with a trialkylpyridine compound, the feed to the oligomerization process may includeadditional trialkyl pyridine compound so that the surface properties ofthe zeolite are maintained during the process. For example, the feedconveniently contains about 1 ppm to about 25 ppm of 2,4,6-collidine.See for example the processes described in U.S. Pat. No. 5,026,933 andU.S. Pat. No. 4,870,038, the entire contents of each of which are fullyincorporated herein.

Product

Lightly branched oligomers, referred to alternatively as substantiallylinear olefins or near linear olefins, are produced by theoligomerization process of the invention. Desired oligomerizationproducts include C₁₀+ substantially linear olefin hydrocarbons. Thecatalytic path for feed comprising propylene, butene, and mixturesthereof provides a long chain which may have one or more lower alkyl(e.g., C₁-C₃ alkyl) substituents along the straight chain.

The substantially linear olefinic hydrocarbon produced by the presentprocess is a olefinic hydrocarbon mixture comprising at least at least 5wt %, such as at least 20 wt %, for example at least 85 wt %, ofmono-olefin oligomers of the empirical formula:C_(n)H_(2n)where n is greater than or equal to 6, said mono-olefin oligomerscomprising at least 20 percent by weight of olefins having at least 12carbon atoms, said olefins having at least 12 carbon atoms having anaverage of from 0.8 to 2.0, such as about 0.8 to about 1.3, C₁-C₃ alkylbranches per carbon chain, measured by nuclear magnetic resonancespectroscopy (¹³C NMR).

In one embodiment, the average degree of branching of the C₈ fraction isin the range of from about 0.90 to about 1.30, such as in the range fromabout 0.95 to about 1.20, for example in the range of about 0.95 toabout 1.05; the average degree of branching of the C₁₂ fraction is inthe range of from about 1.05 to about 1.60, such as in the range fromabout 1.05 to about 1.50, for example in the range of about 1.05 toabout 1.40; and the average degree of branching of the C₁₆ fraction isin the range of from about 1.10 to about 1.70, such as in the range fromabout 1.20 to about 1.60.

The invention will now be more particularly described with reference tothe following prophetic examples.

EXAMPLE 1

A feedstream having the hydrocarbon composition given in Table 1 andcomprising from about 50 wt. % to about 70 wt. % butenes and from about0 wt. % to about 10 wt. % propylene and containing from about 1 ppm toabout 25 ppm of 2,4,6-collidine is passed through a thermostatted watersaturator. The temperature of the feedstock is from about 30° C. toabout 50° C. and the water concentration of the feedstock is from about575 ppm to about 625 ppm. A ZSM-23 catalyst which has been treated with2,4,6-collidine in the manner described in U.S. Pat. No. 5,026,933 isthen used to oligomerize the feed at a temperature of from about 200° C.to about 225° C., a pressure of about 1100 psig (7584 KPa (gauge)) toabout 1400 psig (9653 KPa (gauge)) and a WHSV of from about 1.75 hr⁻¹ toabout 2.25 hr⁻¹. The product of the oligomerization process is composedof from about 40 wt % to about 50 wt % of C₈ olefins, from about 30 wt %to about 40 wt % of C₁₂ olefins and from about 5 wt % to about 15 wt %of C₁₆ olefins. The average degree of C₁-C₃ alkyl branching of the C₈,C₁₂ and C₁₆ fractions is determined by ¹³C NMR and is found to be fromabout 0.95 to about 1.05, from about 1.05 to about 1.40, and from about1.20 to about 1.60, respectively. It is believed that, based on thecondition and reactivity of the catalyst, addition of water to the feedextends the useful life of a catalyst subjected to prolonged practice ofthe process as compared to the useful life of a catalyst with anunhydrated feed subjected to such use.

TABLE 1 From About To About Component (Wt. %) (Wt. %) Ethane 0.03 0.09Propane 0.86 0.91 Propylene 0.14 0.17 Isobutane 23.89 27.46 n-Butane16.20 22.73 Butene-1 20.07 23.88 Isobutylene 0.78 1.07 t-Butene-2 17.9619.98 c-Butene-2 11.71 12.73 Butadiene-1,3 0.00 0.09 Isopentane 0.531.17 Pentene-1 0.00 0.08 Dimethyl Ether 0.07 0.15 MTBE 0.00 0.01 TAME0.00 0.01 Total Butenes 50.81 57.30 Total Pentenes 0.00 0.08

EXAMPLE 2 (COMPARATIVE)

The feedstream in Example 2 is identical to that described in Example 1except that the feed is not passed through a water saturator. Thefeedstream is subjected to the same oligomerization process as set forthin Example 1. The temperature of the feedstock is from about 30° C. toabout 50° C. and the water concentration of the feedstock is from aboutzero ppm to about 5 ppm. The product of the oligomerization processcontains from about 10 wt % to about 50 wt % of C₈ olefins, from about30 wt % to about 40 wt % of C₁₂ olefins and from about 5 wt % to about25 wt % of C₁₆ olefins. The average degree of methyl branching of theC₈, C₁₂ and C₁₆ fractions is determined by ¹³C NMR and is found to befrom about 0.95 to about 1.05, from about 1.05 to about 1.40, and fromabout 1.20 to about 1.60, respectively.

Results indicate that the active catalyst life after completion of theprocess set forth in Example 1 exceeds the active catalyst liferemaining after completion of the process set forth in Example 2.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For example, it is contemplated that anolefin feed is contacted with water vapor. It is also contemplated thatliquid water or water vapor is separately added to the reactor, injectedinto the feedstream or added to the catalyst. For this reason, then,reference should be made solely to the appended claims for purposes ofdetermining the true scope of the present invention.

1. A process for preparing a substantially linear olefinic hydrocarbonmixture comprising the step of contacting a lower olefin feed comprisingone or more C₃ to C₆ lower olefins in the presence of water and underolefin oligomerization conditions with a catalyst comprisingsurface-deactivated ZSM-23, said substantially linear olefinichydrocarbon mixture characterized by having at least two of methyl,ethyl, and propyl branches as measured by ¹³C NMR.
 2. The processaccording to claim 1, wherein said ZSM-23 has been surface deactivatedwith a sterically hindered nitrogenous base.
 3. The process according toclaim 2, wherein the nitrogenous base is 2,4,6-collidine.
 4. The processaccording to claim 1, wherein the feed comprises propylene and butene.5. The process according to claim 4, wherein that the mole ratio ofpropylene to butene in the feed is in a range of about 99:1 to about1:99.
 6. The process according to claim 4, wherein the mole ratio ofpropylene to butene in the feed is in a range of about 49:51 to about5:95.
 7. The process according to claim 4, wherein the mole ratio ofpropylene to butene in the feed is in a range of about 35:65 to about10:90.
 8. The process according to claim 1, wherein the concentration ofwater in the feed is in a range of from about 25 ppm to about 1000 ppm.9. The process according to claim 1, wherein the concentration of waterin the feed is in the range of from about 100 ppm to about 750 ppm. 10.The process according to claim 1, wherein the concentration of water inthe feed is in the range of from about 575 ppm to about 625 ppm.
 11. Theprocess according to claim 1, wherein the water is contacted with thefeed prior to contacting of the feed with the catalyst.
 12. The processaccording to claim 11, wherein the water and the feed are contacted at atemperature in the range of from about 20° C. to about 60° C.
 13. Theprocess according to claim 1, wherein the feed is water-saturated. 14.The process according to claim 1, wherein the oligomerization conditionscomprise a pressure in the range of from about 500 psig (3447 KPa(gauge)) to about 1500 psig (10342 KPa (gauge)).
 15. The processaccording to claim 1, wherein the oligomerization conditions comprise apressure in the range of from about 750 psig (5171 KPa (gauge)) to about1250 psig (8618 KPa (gauge)).
 16. The process according to claim 1,wherein the oligomerization conditions compose a temperature in therange of from about 160° C. to about 250° C.
 17. The process accordingto claim 1, wherein the oligomerization conditions compose a temperaturein the range of from about 190° C. to about 230° C.
 18. The processaccording to claim 1, wherein the oligomerization conditions comprise atemperature in the range of from about 210° C. to about 220° C.
 19. Theprocess according to claim 1, wherein the oligomerization conditionscomprise a weight hourly space velocity of from about 0.1 hr⁻¹ to about4.0 hr⁻¹.
 20. The process according to claim 1, wherein theoligomerization conditions comprise a weight hourly space velocity offrom about 0.2 hr⁻¹ to about 3.0 hr⁻¹.
 21. The process according toclaim 1, wherein the oligomerization conditions comprise a weight hourlyspace velocity of from about 1.75 hr⁻¹ to about 2.25 hr⁻¹.
 22. Theprocess according to claim 1, wherein the substantially linear olefinichydrocarbon mixture comprises at least 85% by weight of mono-olefinoligomers of the empirical formula:C_(n)H_(2n) where n is greater than or equal to 6, said mono-olefinoligomers comprising at least 20 percent by weight of olefins having atleast 12 carbon atoms, said olefins having at least 12 carbon atomshaving an average of from 0.8 to 2.0 C₁-C₃ alkyl branches per carbonchain.
 23. The process according to claim 22 wherein said olefins havingat least 12 carbon atoms have an average of from 0.8 to 1.3 C₁-C₃ alkylbranches per carbon chain.